Patent Literature 1 describes a method for producing an annular core used in an armature. Such an annular core is produced through the following steps.
(1) A plurality of split iron core pieces are prepared.
(2) In a die unit, the plurality of split iron core pieces are formed in an annularly arranged state, the split iron core pieces are further laminated on the annularly arranged split iron core pieces, an annular intermediate body with split cores annularly connected is formed, and the intermediate body is ejected from the die unit. (3) For example, dimensional accuracy of the intermediate body ejected from the die unit is inspected, and when necessary, heat treatment is performed. (4) Each of the split cores is decoupled to disconnect the intermediate body. A winding wire is wound on each of the obtained split cores. (5) The split cores with the winding wires wound are annularly reassembled to obtain the annular core.